Method for making filtering material for tobacco products

ABSTRACT

Method for treating paper to render it particularly adapted to be gathered and enclosed in a wrapper to make a filter cord subdividable into efficient cigarette filters. The paper is first moistened with a volatile, impregnating agent to prevent undue tearing in a longitudinal grooving and lateral stretching treatment which loosens and exposes fibers by passage through the nip between heated meshing rollers having alternating circumferential ribs and grooves. The impregnating agent has a boiling point and heat of evaporation less than those of water to reduce drying time. Coating materials, e.g. cellulose triacetate, cellulose acrylic acetate, may be dissolved in the impregnating agent so that the fibers of the paper will be coated with the material on evaporation of the impregnating agent.

Nov. 23, 1911 R A. MULLER. HAL 3,621,764

METHOD FOR MAKING FILTERING MATERIAL FOR TOBACCO PRODUCTS Filed April 28, 1970 4 Sheets-Sheet l BY zp/flji fggf iiwm TI OR/VEVS Nov. 23, 1971 RA. MULLER ETAL METHOD FOR MAKING FILTERING MATERIAL FOR TOBACCO PRODUCTS Filed April 28, 1970 4. Sheets-Sheet I Fig. 5

//V VE/V 709$ Pin/z. flDOLFMULLEl? Hfl/VS Musra Nov. 23, 1971 P. A. MULLER ETA 3,621,764

METHOD FOR MAKING FILTERING MATERIAL FOR TOBACCO PRODUCTS Filed April 28, 1970 4 Sheets-Sheet 5 k H n u H a c o b c //v VIA/7017.5 P1901 19004; Mf/ALffi HA7 #3 M0375? Nov. 23, 1971 R A. MULLER ETAL 3 ,621,764

METHOD FOR MAKING FILTERING MATERIAL FOR TOBACCO PR'DDUC'I'S Filed April 28, 1970 & Sheets-Sheet 4 //V Ma /V7085 PAM .4 16 001.; fix/452 fi/i ms M03 71 United States Patent METHOD FOR MAKING FILTERING MATERIAL FOR TOBACCO PRODUCTS Paul A. Muller, 9497 Triesenberg 405, Liechtenstein, and Hans Muster, 8340 Hadlikon, Hinwil, Switzerland Filed Apr. 28, 1970, Ser. No. 32,569 Claims priority, application Switzerland, Mar. 24, 1970,

,590/70 Int. Cl. B3ld U.S. Cl. 93l C 40 Claims ABSTRACT OF THE DISCLOSURE Method for treating paper to render it particularly adapted to be gathered and enclosed in a wrapper to make a filter cord subdi'vidable into efiicient cigarette filters. The paper is first moistened with a volatile, impregnating agent to prevent undue tearing in a longitudinal grooving and lateral stretching treatment which loosens and exposes fibers by passage through the nip between heated meshing rollers having alternating circumferential ribs and grooves. The impregnating agent has a boiling point and heat of evaporation less than those of water to reduce drying time. Coating materials, e.g. cellulose triacetate, cellulose acrylic acetate, may be dissolved in the impregnating agent so that the fibers of the paper will be coated with the material on evaporation of the impregnating agent.

The present invention relates to an improved method of making filtering material in the form of substantially continuous, longitudinally grooved fiber-containing webs of material, particularly paper webs having loosened and exposed fibers, which are suitable for being laterally gathered into a bundle. Wrapping this bundle produces an endless filter string or cord which can be divided into filter rods and filter plugs for cigarettes and other tobacco products.

Gathering and wrapping of the longitudinally grooved web of material or paper may be effected directly following its preparation or the longitudinally grooved webs may be wound to form rolls, stored and subsequently supplied to the conventional cording machines for the production of a wrapped filter cord and its subdivision into filter rods.

The term crimped or creped paper normally designates a material which, during production in paper machines, is upset in its direction of travel so that irregular transverse ribs are formed and that the web possesses a greater weight than corresponding paper webs which are not upset. Such crimped papers were formerly largely employed for the manufacture of cigarette filters, but they are diflicult to process since crimping is transverse to the direction of travel of the paper web and, in addition, they provide only a relatively low extracting effect on the solid and liquid particles to be removed from tobacco smoke When used as filters.

0n the other hand, other longitudinally crimped webs of material or paper are known and disclosed in Pats. Nos. 2,995,481, 3,161,557, 3,226,280, in which the crimped grooves run in a direction parallel to the direction of travel of the endless webs. In the manufacture of such longitudinally crimped webs the paper is passed through the nip between a pair of intermeshing metal rolls provided with annular ribs, care being taken that longitudinal grooving of the paper web is efiected at least partly at the expense of the paper thickness. In the process, the web of material cannot move transversely to the direction of travel so that it is stretched in the transverse direction. In this process the paper is advantageously rendered ductile, e.g., as by moistening prior to longitudinal grooving so that the transverse cohesion of the paper web is "ice not destroyed under major transverse stretching although such transverse stretching may be increased so as to produce discontinuous short longitudinal tears in the paper. After the passage between the intermeshing metal rolls, i.e. the longitudinal crimping unit proper, the web of material or paper provided with longitudinal grooves is dried. Such longitudinally grooved webs of material or paper have stood the test of time in the manufacture of filter plugs for cigarettes and are commercially used in a considerable volume.

According to a further development, also known in the art, e.g. Pat. No. 3,466,358 of this process of treating endless webs of a fiber-containing material, particularly paper, for the manufacture of an endless filter cord that can be subdivided into filter rods, the moistened, virtually inelastic web of material is also passed through the nip between two heated grooving and stretching rolls provided with narrow intermeshing annular ribs which do not, however, contact one another so that the web of material is longitudinally crimped and transversely stretched until fibers are loosened and exposed without fully destroying transverse cohesion of the web, and, after emerging from the nip, allowed to rest on at least one of the roll along a given looping angle, simultaneously partially dried over parallel longitudinal zones, stiffened and the loosened structure there fixed. Subsequently the web of material which remains on the said roll may be passed between a second nip between this roll and a third identical roll, taken over by the said third roll and allowed to rest on the same along a looping angle.

This improved method, too, has proven to be successful and thanks to the further deepening of the longitudinal grooves produced in the web of material in the first nip, so that an additional transverse stretching efrect occurs, a more substantially frayed web of material or paper with enhanced filtering efficiency may be produced.

In the said process of making longitudinally crimped webs of material, particularly when using thin paper of about 20 to 50 grams weight per square meter, it is necessary to moisten the web of material before it passes through the first nip between intermeshing rolls provided with annular ribs and consequently afterwards to dry the web of material or paper provided with longitudinal grooves. These two operations involve difiiculties if the travel of the web to be processed is accelerated in order to increase hourly production and accordingly to run the machines involved as economically as possible. In so doing, the space of time available for moistening a centimeter of web length becomes ever shorter and the energy requirements for drying ever greater as the rate of travel of the web increases. By way of example, if moistening of the web in the device designed therefor is effected during the passage over 10 centimeters of travel, the time of dwell of every centimeter of web in the moistening unit is reduced to 0.04 seconds at a rate of web travel of about 240 meters per minute, which no longer sufiices for uniform and accurate moistening. Likewise, the time of dwell in the drying unit provided becomes correspondingly short, which renders necessary the provision of much space for a larger or longer drying apparatus to increase the dwell time or a corresponding increase of energy for the drying operation.

These difficulties are overcome by the present invention which relates to a method of treating endless webs of fiber-containing material, particularly paper, so as to render it suitable for gathering in the transverse direction and wrapping for making an endless filter cord which may be subdivided into filter rods, the virtually inelastic web of material being continuously passed through at least one nip between a pair of rotating grooving and stretching rolls provided with narrow intermeshing annular ribs which do not contact one another, the web of material being held by the annular ribs and stretched transversely to the direction of travel, the said transverse stretching being increased until fibers are loosened and exposed without complete destruction of the transverse cohesion of the material.

The characteristic feature of this invention is the fact that the web of material is treated with a volatile impregnating agent prior to its entry into the nip and that the said agent is removed as the web emerges from the said mp.

In the present context the term volatile impregnating agents refers to organic liquids of which the boiling point is below that of water at the atmospheric pressure present and which have a lower heat of evaporation than water, preferably below 250 cal./ gr.

A number of embodiments of the invention will now be described in greater detail with reference to FIGS. 1 through 10 of the drawing in which:

FIG. 1 is a digrammatic side view of an embodiment of a device for the performance of the method according to this invention;

FIG. 2 is an enlarged fragmentary front view of the intermeshing grooving and stretching rolls of the device according to FIG. 1;

FIG. 3 is a fragmentary side view of the grooving and stretching rolls according to FIG. 2 taken on the line 33;

FIG. 4 is a fragmentary sectional view of the grooving and stretching rolls according to FIG. 3 taken along the line 44;

FIG. 5 is a diagram showing, by percentage increase in draw resistance of filter plugs, the effect of moistening with a volatile impregnating agent T as contrasted to water;

FIG. 6 is a diagram showing the swelling property Q of paper Webs when impregnated with various impregnating agents;

FIG. 7 is a diagram showing the effect of the concentration K of an additive on the tensile resistance Z of filter rods, and

FIGS. 8 through 10 are diagrammatic views of devices for the performance of the method according to the present invention.

The present method will now be described when a web of material formed of smooth unsized paper of 0.06 to 0.07 mm. thickness and to 50 grams weight per square meter is employed, but the method is not limited thereto.

It is essential for the present method that the smooth and fiat paper web to be processed is treated, prior to being crimped in the longitudinal direction and at the same time stretched in the transverse direction in a grooving and stretching process, with a volatile impregnating agent, such as methyl alcohol which is removed by vaporization or volatilization subsequent to the grooving and stretching process.

A web formed of a fiber-containing material, such as paper, processed according to this method displays a frayed structure and possesses a plurality of short, discontinuous teantype openings which run preferably in the longitudinal direction. The mechanical strength of the web of material in the longitudinal direction is, however, sufficient to ensure that no breakage need be feared as it passes through a cording machine for the production of an endless filter cord which may be subdivided into filter rods. The entire fiber-containing web of material, preferably the zones with holes or heavy thinning of the material thickness, possesses loosened and exposed fibers which provide a filter plug containing such a web of material gathered in the transverse direction with a high degree of filtering efliciency. The longitudinal crimping of such a web of material not only facilitates gathering in the transverse direction into a continuous cord as the web passes through the cording machines, but also ensures the desired uniformity of the stuffing of such a filter cord in the transverse direction. With a longitudinally crimped paper web of the structure indicated, the undesirable softening of the filter content during use is avoided and the elasticity of the filter plugs in the transverse direction is adequate also during smoking.

Prior to producing the longitudinal grooving and the simultaneous transverse stretching, the Web of material, by way of example the smooth raw paper web made of only slightly ground fibers, must first be impregnated with a volatile liquid, e.g. methyl alcohol. This may be effected by moistening the web of material by way of example by spraying, dipping or other methods known to the paper fabricating industry. However, a continuously operating process must be employed since the grooving and stretching processes have to be performed at high speeds.

The grooving and stretching processes on the moistened material are effected during the continuous travel of the web of material through grooving and stretching rolls which will be described in greater detail below. It is assumed that, during the passage of a moistened paper web through such grooving and stretching rolls, the paper is more or less firmly held at a plurality of transversely adjacent points and stretched and elongated in the transverse direction in the intermediate areas because the longitudinally crimped paper web indeed reveals clearl recognizable parallel longitudinal zones and grooves and ribs in the longitudinal direction. At all events the grooving and stretching treatment greatly increases the surface of the.

material in certain areas at the expense of the thickness of the material, which is of importance for the enhancement of filtering efficiency. By way of example, it is possible to perform the grooving and stretching processes in such a manner that the longitudinally grooved paper web has virtually the same width as it emerges from the crimping unit as the raw paper web had when entering it so that shrinking in the transverse direction is avoided.

After the grooving and stretching treatment of the previously moistened web of material or paper, a drying process is necessary in order again to stiffen the longitudinally crimped web and to fix the loosened structure. After complete drying, the paper web longitudinally crimped according to the present method may have a greater width than the smooth raw paper as supplied to the crimping unit after being impregnated with a volatile liquid. This is where the present method dilfers from the known processes in which water is used for moistening. It is Well known and can be observed in the manufacture of longitudinally crimped paper webs that the webs emerging from the crimping unit possess virtually the same width as the moistened raw paper, but that they contract more or less markedly in the transverse direction during the passage through the drying unit when they reach a certain degree of dryness. Compared with the width of the raw paper webs, the so-called shrinkage factor of the dried longitudinally crimped paper web may be as high as 30%. The raw paper impregnated not with water but with methyl :alcohol, however, behaves quite differently and after complete drying reveals widening relative to the raw paper web by a so-called expansion factor of 30% and more.

By way of example, if a raw paper smooth on one side weighing 38 grams per square meter is employed, which has an average fiber length of 2 to 4 mm. and of which the fibers have been only slightly ground and, respectively, beaten, a strip of such paper 10 cm. wide will produce, after passage through a crimping station of the design described below with reference to FIGS. 2 through 4 and with unmodified setting of the roll engagement depth:

When moistening with water, a width of the longitudinally crimped strip of Cm. In moist condition 9.8 In dry condition 7.0

When moistening with methyl alcohol, a width of the longitudinally crimped strip of Cm. In moist condition 10.0 In dry condition 12.8

Accordingly the contraction factor with water was about 30% but the widening factor with methyl alcohol about 28%.

The longitudinally crimped paper webs made according to this method, however, do not only reveal stretching instead of the shrinking observed after moistening with water, but the structure of the paper webs so treated is different. Despite the identical setting of the roll engagement depth and the same dimensions of the crimping rolls employed a substantially greater number of tear-type holes is apparently produced which are, however, largely shorter so that the impression of greater fraying is created. Accordingly, a paper web so produced has a considerably softer touch and appears to possess a velvety fibrous surface.

placed by methyl alcohol. The filter rods produced were as usual first tested for their resistance to pulling (draw resistance) and then subdivided into 6 filter plugs mm. long each, which were mounted on the tobacco cylinder of the same filterless cigarette brand and then smoked in a standardized smoking machine; the fraction of liquid and solid particles of tar and nicotine (in milligrams) contained in the smoke behind the filters was determined and the mean value calculated from every 10 such measurements. The following values were obtained:

Filter rods and filter plugs made Paper webs impregnated Paper webs with methyl impregnated alcohol with water Resistance to pulling (mean value from 10 filter rods), mm. WC 280 113 Quantity of particles in the smoke behind the filter, per cigarette, mg.. 8 18 The difference between the resistance to pulling alone reveals that the fraying of the paper web essential therefor is considerably greater. Despite the same quantity of paper in the filter rods compared an increase of the resistance to pulling by about 115% was determined for webs processed according to this invention.

The filter plugs of which each contained the same quantity of paper accordingly reveal a substantially greater extracting effect of the paper treated according to the present method; consequently, the use of methyl alcohol as an impregnating agent cannot have caused the surface of the fibers contained in the paper and loosened or exposed by the crimping and transverse stretching process to undergo any detrimental effect. On the contrary it is suspected that the cleansing action of a volatile impregnating agent, such as methyl alcohol, increases the adsorptive capacity of the fibers for the particles to be separated from the smoke.

The measuring results above described were achieved by employing methyl alcohol as a volatile impregnating agent. In addition, other alcohols, such as ethyl alcohol (ethanol) and propyl alcohols (propanols) are suitable as well. Other very useful impregnating agents are acetone and other ketones. Again, diethyl ether and other ethers such as sulphuric ether and sodium ether may be employed. Moreover, cyclic ring compounds such as Xylenes, toluene, benzene, mixtures such as light gasolines and so-called aromatic ring compounds may be used as impregnating agents. Halide hydrocarbons, such as ethyl chloride, chloroform, carbon tetrachloride and the like, may be used as well as esters such as acetic acid ethyl ester (ethyl acetate).

All impregnating agents are suitable for the present method that have a boiling temperature lower than that of water and evaporation heat below about 250 cal/gr.

The effect of a solution of pure alcohol and water on the shrinking and stretching factor of longitudinally crimped paper webs in drying is shown by the table below which relates to raw paper strips made of the abovementioned paper quality:

Width of the paper webs prior to After impregnadrying, Impregnatiug liquid tiou, mm. mm

Pure water 120 90% Water plus 10% alcohol 120 50% water plus 50% alcohol 120 10% water plus 90% alcohol... 120 Pure alcohol 120 168 The paper web 1 passes through a station that moistens it. In the present embodiment the said station comprises a rotating roll 5 which dips into a volatile liquid 6 and in operation has its surface provided with a liquid film which moistens the underside of the paper web 1 passing through. The counter-roll 7 consisting, by way of example, of a resilient material forces the paper web against the rotating roll 5. Shallow or deeper immersion of the roll 5 in the impregnating bath 6 and regulation of the contact pressure of the roll 7 enables the moistening of the passing paper web to be adjusted within certain limits. It is advantageous to select the degree of moistening so that the paper still possesses adequate tearing resistance in its longitudinal direction so that it may pass the downstream stations of the device shown in FIG. 1 wtihout breaking. On the other hand however, the paper web must be impregnated sufiiciently to allow corresponding transverse stretching for the desired degree of longitudinal crimping.

Upon leaving the moistening unit the web of material passes into a grooving and stretching unit and there first runs into the nip between the grooving and stretching rolls 8 and 9. Each of the two rolls is provided with a plurality of closely adjacent annular ribs which intermesh by an adjustable value without contacting one another.

Depending on the type of the volatile impregnating agent employed, it may be advantageous to heat the grooving and stretching rolls 8, 9 and also the grooving and stretching roll 10 to be described later to a certain temperature which may naturally be only so high that the vapors emerging from the paper web cannot ignite. To this end, the rolls may be provided with suitable electrical heating elements in their interior which are either stationary or supplied through the hollow shafts of the said rolls, or then rotate along with the rolls so that power supply must be effected via exterior slip-rings. Heating may naturally be etfected also by other suitable means, by way of example by hot steam which flows through the hollow rolls. It is important in this context that the temperature cannot rise above an admissible maximum value; the heating equipment, however, must be capable of keeping the grooving and stretching rolls at the desired temperature also at passage rates of the impregnated paper web up to several meters per second.

As the moistened paper web passes through the nip between the grooving and stretching rolls 8 and 9, it is apparently retained somewhat at the spots contacting the ribs so that transverse stretching is particularly pronounced in the zones between the said adhering areas of the paper. At all events, the paper passing through the nip between the rolls 8 and 9 reveals parallel, strip-type longitudinal zones of different structure which are clear ly visible in the paper web.

For the adjustment of the meshing depth of the two grooving and stretching rolls 8 and 9 it is advantageous for the axis of rotation of the roll 8 to be adjustable relative to the axis of rotation of the roll 9. This adjustment, however, must be effected, by way of example, by two jointly driven spindles carrying the shaft of the roll 8 at each end so that it is ensured that, in the event of the height of the shaft of rotation of the roll 8 being adjusted, the said shaft remains accurately parallel with the axis of rotation of the roll 9. Height in its turn must be so finely adjusted that it is possible to adjust the meshing depth of the associated annular ribs, approximately in the range between and 1 mm. meshing depth, to fractions of a tenth of a millimeter, accurately and reproduceably. It is advantageous for the adjusting device to be provided with a calibrated scale and markings so as to ensure that a desired meshing depth can at any time again be set if such depth has been changed for any reason. In addition, the grooving and stretching roll 8 can be adjusted on its shaft of rotation in the axial direction so that the annular ribs of the roll 9 can be accurately placed in the middle of the annular grooves of the roll 8. It has also been found that axial displacements of the roll 8 relative to the roll 9 appear to be capable of changing the character of the longitudinal crimping in the paper web.

The paper web passing through the nip between the grooving and stretching rolls 8 and 9 comes to rest, after emerging from the said nip, on the surface of the roll 9, in the present embodiment along a looping angle of about 180, and then passes into the nip between this roll 9 and a third grooving and stretching roll 10. During the dwell of the paper web already grooved and transversely stretched on the surface of the roll 9, the portions of the paper web in contact with the annular ribs of the said roll are somewhat dried and stiffened so that the loosened structure of the paper produced in the first grooving and stretching zone is fixed and so that no hazard remains that this structure may be adversely affected by the softness and resilience of the paper.

The grooving and stretching roll 10 is provided with similar annular ribs and rotates about an axis of rotation which is parallel with that of roll 9. The rotating shaft of the roll 10 is adjustable in height relative to that of roll 9 and, moreover, a slight axial adjustment of the roll 10 on its shaft of rotation is allowed for in a manner similar to that described in connection with the grooving and stretching roll 8.

As the previously longitudinally crimped and, to a certain extent transversely stretched paper web passes through the second nip between the intermeshing rolls 9 and 10, further deepening of the longitudinal crimping and an increase in the transverse stretching may be achieved, it being ensured that the position of the paper web in the second nip between the rolls 9 and 10 is the same as between the rolls 8 and 9. After emerging from the second nip the paper web now longitudinally crimped and transversely stretched in two steps comes to rest, along a looping angle of 180, on the roll 10 and is thence drawn off in the horizontal direction via a guide roll 11. Mention should be made of the fact that, while the paper web remains on the roll 10, such portions contact the heated annular ribs as were located between adjacent annular ribs during the passage of the looping angle of the roll 9 and which did thus not contact the annular ribs of the roll 9. This ensures that the paper web drawn off the roll 10 is similarly predried and stiffened on its upper side and underside.

If desired, the crimping unit comprising the three rolls 8, 9 and 10 may be provided with a covering hood 14 so that the vapors emerging from the paper web can escape or be drawn off in the upward direction as indicated by arrow 15.

The paper web thus longitudinally crimped and transversely stretched in two steps is in most cases completely freed from the liquid it contains by the contact with the two rolls 9 and respectively, 10. In the event that such drying is inadequate, the paper web may be supplied, via the guide rolls 11 and 12, to a further drying device 13 which removes the residual liquid contents of the travelling longitudinally crimped paper web in the known manner, i.e. by electrical heating or hot air. When the volatile impregnating agents are employed according to the present method, however, it is possible to dispense with such an additional drying unit 13 since the drying effect of the two heated rolls 9 and 10 suffices fully to dry the longitudinally crimped paper web.

Against the great energy requirements of the processes operating with water moistening so far known in the art, the only low energy requirements for evaporating the 'volatile impregnating agents constitutes an essential ad vantage of the present method.

If desired, the impregnating agent evaporating from the paper web may also be reclaimed, to which end known devices may be arranged on the suction tube of the hood 13.

The embodiment of FIG. 1 of a device for the performance of the present method of making longitudinally crimped and transversely stretched fiber-containing material may be equipped with a take-up unit of a design generally known which winds the longitudinally crimped paper web into rolls. But it is also possible to supply the longitudinally crimped paper web made directly into the gathering unit of a cording machine of known design. It may here sometimes be of advantage for the paper web not to be completely dried and to dry out after wrapping and subdivision into filter rods. The present method is advantageous particularly for high-speed cording machines which should directly be supplied with longitudinally crimped paper webs because the fast removal of the volatile impregnating agent from the longitudinally crimped paper web is possible without difliculty.

Instead of the grooving and stretching station equipped with three intermeshing rolls 8, 9 and 10 according to FIG. 1, stations of some other design may be provided as described in Pat. No. 3,466,358 (application for patent No. 7,599/67). I

The rolls employed for the present grooving and stretching process are preferably equipped with annular ribs ha ving flat flanks normal to the roll axis and with substantially rectangular cross-section with cylindrical faces which preferably form sharp edges with the flanks. By way of example, annular ribs have proved to be of advantage which are spaced by 0.7 mm. and have a thickness of 0.3 mm. with a radial flank height of about 1.0 to 1.5 mm. Since the grooving and stretching operation is preferably-but not exclusively-performed with fiber-containing flat material of a thickness below 0.1 mm., by way of example with raw paper with a mean thickness of about 0.07 mm., the web paper passes through the nip between a pair of rolls having such annular ribs which intermesh to a depth of e.g. 0.5 mm. without contacting the side flanks of the ribs if the ribs of one roll extend accurately in the middle of the groove between the two opposite rolls. With the said dimensions each of the intermeshing annular ribs has a lateral distance of 0.2 mm. and a paper web passing through this nip will contact the said annular ribs only on their cylindrical faces.

The grooving and stretching operation for the performance of the present method may also be performed with only two intermeshing rolls provided with annular ribs, but the stress exerted on the paper web is so brief and violent that the individual fibers may break or tear. This is why a crimping station having more than two intermeshing rolls is preferably employed, e.g. as shown in the embodiment according to FIG. 1.

A preferred embodiment of the grooving and stretching rolls also used according to the present method is shown in FIGS. 2 through 4 at a scale enlarged by about 10:1, the diameter of the rolls being shown smaller than in reality for convenience. The three intermeshing grooving and stretching rolls 8, 9 and 10 are identical in respect of their annular ribs 21 and the annular grooves 20 formed therebetween. The annular ribs 21 of the rolls 8 and 10 engage with the associated annular grooves 20 of the roll 9. As indicated in FIGS. 2 and 3 the paper web 1 passes through the tortuous nip between the intermeshing annular ribs. The degree of meshing between the lower roll 8 and the center roll 9 is preferably set smaller (not shown in the drawing) than that between the annular ribs of the upper roll 10 and the center roll 9 so that the lower nip has a shallower mesh and the upper nip a deeper one. By way of example, engagement of the lower nip may be about 0.3 mm. while the upper nip has an engagement depth of about 0.6 mm. Engagement is indicated along the connecting line between the axes of the rolls 8 and 9 and respectively, of the rolls 9 and 10. The passing paper web is thus longitudinally crimped in two successive steps and at the same time stretched transversely, those zones Of the paper web that contact the cylindrical faces of the ribs 21 of the roll 9 in the passage through the first nip between the rolls 8 and 9 remaining on the said ribs after emerging from the said nip until they pass into the second nip between the rolls 9 and 10. The paper web remains on the roll 9 for a space of time corresponding to the looping angle of 180. After the passage through the second nip between the roll 9 and 10, the more deeply crimped and more strongly stretched paper web remains on the roll 10 for a looping angle of again about 180, such longitudinal zones contacting the flat faces of the annular ribs 21 of the roll 10 that did not contact the annular ribs of the roll 9 while they rested there.

The two-stage grooving and stretching operation with the rolls as per FIGS. 2 through 4 enables the paper to be reliably grooved longitudinally and transversely stretched without excessive stress on the paper also when the rate of web travel is increased. The rolls 8, 9 and 10 being heated to a desired temperature, such longitudinal strips of the paper as contact the faces of the said annular ribs are to a certain extent dried and stiffened which has for a consequence that the paper meets requirements during the subsequent grooving and stretching operation in the second nip. Appropriate adjustment of the engagement depth between the associated annular ribs in the first and second nips enables a longitudinally crimped and transversely stretched paper web to be obtained which meets a plurality of requirements without in any way adversely affecting the paper structure.

It may also be pointed out that a paper web resting on one of the grooving and crimping rolls during a predetermined looping angle is subjected to bending which is advantageous for loosening and exposing of individual fibers. In a grooving and crimping station formed of the three rolls 8, 9 and 10, bending of the longitudinally crimped web of material is effected first in one and then in the other direction, which facilitates the exposure of individual fibers.

As previously mentioned, most of the volatile impregnating agents recited above possess the property that they cause a widening of the longitudinally crimped and frayed paper webs during the drying process as opposed to the shrinking of the paper webs moistened with water. Accordingly the use of volatile impregnating agents, such as alcohols and ketones, which can be diluted with water enables the width of the longitudinally crimped paper web after drying to be influenced by a greater or lesser addition of water.

By way of example, if a device of the design described for making longitudinally crimped webs of material is em ployed to provide a paper web of a predetermined width with longitudinal grooves, at the same time stretching it in the transverse direction and fraying it so that the said paper web can then be directly supplied to a commercial cording machine for producing wrapped paper filter rods, the resistance to pulling of the filter rods made may be influenced by greater or lesser water addition to the volatile impregnating agent. By way of example, a raw paper web 240 mm. wide, weighing 35 grams per square meter and 0.06 mm. thick was processed in such a device into filter rods of 0.8 mm. diameter and 102 mm. length, the impregnating agent employed having been a mixture of methyl alcohol and water. The resistance to pulling of the filter rods was determined by the usual standardized method in mm. water column with the passage of a volume of air of 17.5 cm. per second. The result (average of 20 filter rods) is shown by curve A in the diagram of FIG. 5 which indicates, along the abscissa, the percentage weights of water W and, respectively, methyl alcohol T in the impregnating agent while the ordinate shows the increase Z of the resistance to pulling in percent against that produced by moistenir'lg with pure water (100% W, T). The curve B in the same diagram shows the in crease in the resistance to pulling Z when a mixture of acetone T and water W (in parts by weight) was used.

Where filter rods are employed in machines for making filter-tipped cigarettes, the mechanical properties, particularly the strength, of the cylindrical filter rods against radial compression and the complete filling of their diameter are of importance. In filter rods made according to the example described above in conjunction with FIG. it has been found that the mechanical strength against radial pressure remains constant within about to if the impregnating agent has a water content of to 100 percent by weight. It has further been observed that the paper web is positively widened in drying where the impregnating agent has a water content between 50 and 0 percent by weight so that it is admissible for the web of material supplied to the cording machine not to be completely dried; during postdrying the paper web inside will expand a little and thus ensure particularly uniform filling of such filter rods.

Examination of the filtering efficiency of filter plugs made by subdividing the filter rods according to the above examples and attached to cigarettes have confirmed the rule, already known, that the filtering efficiency is proportional to the resistance to pulling. At all events treatment of the raw paper with a volatile impregnating agent has no adverse effect on the absorptive and adsorptive power of the exposed paper fibers. Despite these results, however, it was found that the paper webs moistened with volatile impregnating agents prior to longitudinal crimping differ in respect of their water or water vapor absorption from the stream of smoke.

It was first found that the swelling capacity of paper webs differs depending on the water content of the volatile impregnating agents employed. The swelling capacity Q in percent was determined by means of measuring instruments of known design for ten superposed raw paper samples of the same origin which Were compressed by a cylindrical ram of 16 mm. diameter with a weight of 300 grams. The diagram of FIG. 6 shows the swelling capacity Q in percent of two paper types C (38 grams/ sq. meter) and D grams/ sq. meter) when three different impregnating agents were used for moistening, i.e.:

a:pure water 11:50 percent by weight water and percent by weight methyl alcohol c=pure methyl alcohol.

It can be seen that a difference of about 10:1 in terms of swelling capacity exists between water and pure methyl alcohol. Similar differences were also noted in respect of the steam absorption capacity from a gas stream. The ditferent behaviour of such longitudinally crimped and highly frayed paper webs regarding water and steam absorption, however, is of great importance in their use for cigarette filters since it is undesirable excessively to dry the smoke passing therethrough by great water absorption because that will adversely affect the smokes taste. It has long since been known that paper filters, despite their good filtering properties, i.e. great extraction of tar and nicotine substances from the smoke, will produce undesirable modifications of taste owing to excessive moisture absorption and consequent drying of the smoke. Paper webs treated not with water but with volatile impregnating agents according to this method prior to longitudinal crimping and fraying avoid strong drying of the smoke without reducing the desired high degree of absorption of tar and nicotine substances. This improvement may possibly be connected with the fact that the absorption rate of water and, respectively, steam is markedly lower with paper webs treated with volatile impregnating agents than with paper webs moistened with water in longitudinal crimping and fraying.

As stated previously, it is an advantage of the present method that, in employing volatile impregnating agents, additional substances may be dissolved in the said agent which are then placed in fine dispersion on the paper web together with the impregnating agent and left there after drying.

By way of example alcohols as impregnating agents were given additions of tartaric acid, citric acid and similar multivalent oxycarbon acids and filters were produced which improved the taste when the cigarettes were smoked.

Where acetone and other volatile ketones are employed as impregnating agents, cellulose triacetate, cellulose acrylic acetate, cellulose nitrate, cellulose hydroxide and other cellulose compounds, and, respectively, residual glycoses may be dissolved in the impregnating agent as additional substances. The said cellulose compounds or residual glycoses are also suitable as additions for an impregnating agent from the group of organic ethers.

Also suitable are the volatile impregnating agents for dissolving in them such additional substances as causes a chemical reaction, at least on the surface, with the fibers of the web of material.

By way of example alcohols as impregnating agents may be provided with an addition of monovalent oxycarbon acid such as oxyformic acid or oxyacetic acid. Organic ethers as impregnating agents enable monovalent fatty acids such as formic acid, acetic acid, propionic acid and the like to be added.

In the operation of the above-mentioned device using volatile impregnating agents in which additional substances are dissolved, it has in many cases proved to be disadvantageous that in extended operation, such additions are deposited on the grooving and stretching rolls, which is undesirable. In such cases it is of advantage to perform the present method in two consecutive steps. In the first step the raw paper is treated with an impregnating agent which contains the desired substances in solution and then dried. The paper web so impregnated is then moistened with a pure, readily volatile impregnating agent, supplied to the possibly heated grooving and stretching rolls and subsequently freed from the impregnating agent. It has been found that no noticeable residues are formed on the grooving and stretching rolls in this twostage operation even after extended operation.

By way of example, if acetone with a content of a few percent cellulose triacetate is employed, a frayed paper web excellently suited for cigarette filters can be obtained which, however, causes undesirable deposits to be formed on the grooving and stretching rolls in continued operation. This heavily frayed paper web with a cellulose triacetate content excellently suitable for use in cigarette filters, however can advantageously be produced in two steps. In the first step the raw paper web is impregnated with a volatile solution consisting of acetone in which a small quantity, by way of example 0.2 to 4 percent by weight of cellulose triacetate is dissolved. Impregnation and subsequent drying take place very rapidly and require only little energy. The raw paper so impregnated is then moistened with a volatile impregnating agent in the manner above described and supplied to the grooving and stretching rolls; it is advantageous to use an alcohol as the volatile impregnating agent in which cellulose triacetate is not soluble. At all events it has been shown that no undesirable residues are produced on the grooving and stretching rolls by a paper so impregnated. An alcohol-acetone mixture is also serviceable as the moistening agent.

The use of additional substances dissolved in volatile impregnating agents or by previous impregnation of the raw paper web with the appropriate additional substances in very dilute solutions enables highly frayedwebs of material, particularly paper webs to be made which carry the said additional substances on their surface in extremely fine dispersion. Surprisingly, it has been found that in using volatile solvents as impregnating agents an entirely uniform distribution of the additional substances over the entire surface of the paper webs can be obtained and that the subsequent longitudinal crimping and heavy fraying will in no way change this uniform distribution.

By way of example the raw paper webs C and D described above with reference to the diagram of FIG. 6 were impregnated with a solution of about 1 percent by weight of cellulose triacetate in acetone and then dried. The swelling capacity of the raw paper C after such impregnation and subsequent moistening and drying with water and methyl alcohol, respectively, is indicated at E in FIG. 6 and the swelling capacity of the raw paper web D after such treatment at F. It can be seen that the impregnated paper webs show only an extremely low swelling capacity after being moistened with water. On the other hand the swelling capacity after moistening with methyl alcohol is identical with, or greater than, the non-impregnated paper webs. This reveals that, despite the distribution of the acetone solution containing only 1% cellulose triacetate over the entire surface of the paper web the behaviour of the paper fibers towards water is greatly influenced.

Similarly impregnated paper webs 240 mm. wide corresponding to the quality indicated for E and F in FIG. 6 show, after longitudinal crimping and fraying with the use of alcohol as the volatile impregnating or moistening agent, subsequent drying and further processing into filter rods or cigarette filters, a substantially different behaviour than do cigarette filters made of the same raw paper but without the said first impregnation with 1 percent by weight of cellulose triacetate in an acetone solution. It was found in several tests that such cigarette filters obviously remove only small quantities of moisture from the smoke and apparently retain the volatile aromatic substances contained in the smoke much less than corresponding filters made of non-impregnated i.e. with cellulose triacetate, paper webs. At all events the generally known complaints regarding detrimental effects on the taste in smoking the cigarettes occur no longer or only to a very reduced degree as compared with conventional filters in practical smoking tests.

As previously stated the use of the said volatile impregnating agents according to the present method enables an exceptionally fine distribution of additionally desirable substances over the entire surface of the webs of material to be achieved. By way of example, the diagram in FIG. 7 reveals the influence of the concentration of cellulose triacetate as an addition to an acetone solution for the impregnation of raw paper webs of the paper quality described in FIG. 6 under D and F. In the manner de scribed above, filter rods were made with paper webs so impregnated, using methyl alcohol as a volatile moistening agent for the impregnated paper. With the said filter rods, a pulling resistance Z of 200mm. water column was 13 measured for a paper web without any impregnation with cellulose triacetate. The course of the pulling resistance after impregnation with an acetone solution with an increasing percentage K of cellulose triacetate is indicated by curve G and it can be seen that even with as little as 0.5 percent by weight of cellulose triacetate in the acetone solution the resistance to pulling of the filter plugs made drops from 200 mm. water column to about 125 mm. water column. As the concentration of cellulose triacetate increases above about 2 percent by weight, only a small modification of the resistance to pulling is observed. While curve G indicates the influence of impregnation of the raw paper web for filter rods made in two successive steps, the curve H plotted in FIG. 7 for comparison shows the influence of the concentration of cellulose acetate in acetone, if the said solution is used directly as a volatile impregnating or moistening agent for the previously non-impregnated identical paper web.

In the performance of the present method in two successiye steps impregnation may be effected, by way of example, in a device such as diagrammatically shown in FIG. 8. The raw paper web 1 supplied from the roll 2 is passed around a guide roll 20 and a dipping roll 21 which rotates into an impregnating solution 22 in the container 23. The impregnated paper web then passes over the guide roll 24 biased by the roll 25 which may consist of an elastic material so that an excess of impregnating solution is squeezed off. The impregnated paper web subsequently passes through a drying station 26 in which the solvent of the impregnating solution 22 may be reclaimed and is taken up by the supply roll 27 after drying. The paper web so impregnated may be processed into a longitudinally crimped, heavily frayed paper web by means of the device shown in FIG. 1 and described above. Instead of the impregnation method by dipping the paper web into an impregnating solution 22 as shown, impregnation may naturally also be effected by any other known method, by way of example by spraying the impregnating solution on one or both sides of the paper web.

Since the impregnating solution preferably consists of a volatile solvent, drying of the impregnated paper web is effected very rapidly. Accordingly, it is also possible, as diagrammatically shown in FIG. 9, to effect impregnation directly prior to processing the impregnated raw paper by a device according to FIG. 1. The paper web 1 delivered by the supply roll 2 may then pass e.g. between the rolls 30 and 31 and be impregnated by the liquid film taken up by the roll 30 from the impregnating bath 32 in container 33. A drying station 34 then dries the impregnated paper web which subsequently passes directly into the moistening device 5, 6, 7 as previously described with reference to FIG. 1.

Owing to the very fast drying of the longitudinally crimped webs of material, particularly paper impregnated with volatile impregnating agents, the present method enables a device according to FIG. 1 to be directly connected to a high-speed cording machine of conventional design as diagrammatically shown in FIG. 10. The longitudinally crimped web of material and, respectively, paper 40 largely freed from the impregnating agent and running over the guide rolls 11 and 12 is directly fed into the inlet funnel 41 of the said cording machine along with the wrapping band 48 supplied from the drum 47. From the funnel 40 the longitudinally crimped web, which is gathered in the transverse direction, emerges as a wrapped cylindrical cord of e.g. 8.0 mm. diameter; the projecting edge 42 of the wrapper is provided with a strip of glue in the device 43, turned over and fastened during its passage through the heated moulding tool 44 so that the wrapped finished filter cord 49 is formed. To overcome friction, the endless conveyor belt 46 passes around the guide rolls 45 and through the funnel 41 and the moulding tool 44. The finished endless filter cord 49 is then commonly divided into filter rods which usually have a length of 66 to 120 mm. corresponding to six times the length of a filter plug.

It may here be mentioned that, thanks to the use of volatile impregnating agents, the present method is particularly suitable for adding so-called flavoring substances to the said impregnating agents, which is at times desirable.

What is claimed is:

1. A method of treating endless webs of fiber-containing material, particularly paper, to make it suitable for being gathered in the transverse direction and wrapped for the purpose of making an endless filter cord divisible into filter rods, the virtually inelastic web of material being passed through at least one nip between a pair of rotating grooving and stretching rolls equipped with close intermeshing annular ribs which do not, however, contact one another, the web of material being held by the annular ribs and stretched in a direction transverse to that of travel, the said transverse stretching being increased to the point of loosening and exposing fibers without complete destruction of the transverse cohesion of the material, characterized in that the web of material is treated, prior to its entry into the nip, with a volatile impregnating agent and freed thereof upon emerging from the said nip.

2. A method according to claim 1 characterized in that the impregnating agent has a heat of evaporation of less than 250 cal./gr.

3. A method according to claim 1 characterized in that the impregnating agent is selected from among the group including methyl alcohol, ethyl alcohol, and a propyl alcohol.

4. A method according to claim 1 characterized in that the impregnating agent is a volatile ketone.

5. A method according to claim 1 characterized in that the impregnating agent is an ether.

6. A method according to claim 1 characterized in that the volatile impregnating agent is selected from among the group of liquids consisting of benzene and light gasoline.

7. A method according to claim 1 characterized in that the volatile impregnating agent is an halide hydrocarbon.

8. A method according to claim 1 characterized in that the volatile impregnating agent is an ester.

9. A method according to claim 1 characterized in that the impregnating agent is capable of being diluted in water and capable of widening the longitudinally crimped web of material when the latter is freed of the agent as com pared with the uncrimped web of material, and including the step of adjusting the desired degree of widening by adjusting the degree of dilution.

10. A method according to claim 9 for paper webs of 20 to 50 grams weight per sq. m., characterized in that the paper web is impregnated with a mixture of an alcohol and water.

11. A method according to claim 9 for paper webs of 20 to 50 grams Weight per sq. m., characterized in that the paper web is impregnated with a mixture of a ketone and water.

12. A method according to claim 1 characterized in that the impregnating agent is capable of exercising a cleansing action on the surface of the loosened and exposed fibers of the longtiudinally crimped paper web thus enhancing their absorptive power for liquid and solid particles from the smoke.

13. A method according to claim 1 characterized in that the volatile impregnating agent is capable of causing a reduction of the swelling capacity of the longitudinally crimped web of material in the presence of water.

14. A method according to claim 1 characterized in that the volatile impregnating agent is capable of causing a reduction in the rate of absorption of the longitudinally crimped web of material.

15. A method according to claim 1 characterized in that the volatile impregnating agent is capable of causing a reduction of the absorption of steam from the stream of smoke by the web of material.

16. A method according to claim 1 characterized in that the volatile impregnating agent is capable of facilitating exposure and loosening of the fibers of the web of material from the web plane when the said web passes between the grooving and stretching rolls.

17. A method according to claim 1 characterized in that an additional substance is dissolved in the impregnating agent, is applied to the paper web in the finest dispersion, and remains there after drying.

18. A method according to claim 17 characterized in that the impregnating agent is an alcohol with an addition of a multivalent oxycarbon acid.

19. A method according to claim 17 characterized in that the impregnating agent is acetone with an addition from the group of substances consisting of cellulose triacetate, cellulose acrylic acetate, cellulose nitrate, and cellulose hydroxide.

20. A method according to claim 17 characterized in that the impregnating agent is a ketone with an addition from the group of substances consisting of cellulose triacetate, cellulose acrylic acetate, cellulose nitrate, and cellulose hydroxide.

21. A method according to claim 17 characterized in that the impregnating agent is an ether with an addition from the group of substances consisting of cellulose triacetate, cellulose acrylic acetate, cellulose nitrate, cellulose hydroxide, the group of organic acids, such as waxes, and the group of multivalent alcohols, such as glycerin and glycol.

22. A method according to claim 1 characterized in that additional substances are dissolved in the impregnating agent which cause a chemical reaction on at least the surface of the fibers of the web of material.

23. A method according to claim 22 characterized in that the impregnating agent is an alcohol with an addition of a monovalent oxycarbon acid, such as oxyformic acid and oxyacetic acid.

24. A method according to claim 22 characterized in that the impregnating agent is given an addition of a monovalent fatty acid, such as formic acid, acetic acid and propionic acid.

25. A method according to claim 1 characterized in that the impregnating agent evaporated from the paper webs in drying is reclaimed.

26. A method according to claim 1 characterized in that the web of material is impregnated and dried, prior to processing with a volatile impregnating agent, with a liquid which contains dissolved substances which remain on the web of material as a coating after drying.

27. A method according to claim 26 characterized in that the impregnating solution is acetone with an addition of substances from the group consisting of cellulose acetate, cellulose acrylic acetate, cellulose nitrate, and cellulose hydroxide.

28. A method according to claim 26 characterized in that the impregnating solution is a ketone with an addition of substances from the group consisting of cellulose acetate, cellulose acrylic acetate, cellulose nitrate, and cellulose hydroxide.

29. A method according to claim 26 characterized in that the impregnating solution is an ether with an addition of substances from the group consisting of cellulose acetate, cellulose acrylic acetate, cellulose nitrate, and cellulose hydroxide.

30. A method according to claim 1 characterized in that the web of material is impregnated and dried, prior to processing with a volatile impregnating agent, with a liquid which causes a reaction on the fibres of the web of material, at least on their surface.

31. A method according to claim 30 characterized in that the impregnating solution consists of an alcohol with an addition of a monovalent oxycarbon acid, such as oxyformic acid and oxyacetic acid.

32. A method according to claim 30 characterized in that the impregnating solution is an ether with an addition of a monovalent fatty acid, such as formic acid, acetic acid, and propionic acid.

33. A method according to claim 1 according to which the web of material is supplied, after its passage between the grooving and stretching rolls, to a cording machine in which it is transversely gathered into a cylindrical cord, provided with a wrapper, and made into filter rods of a certain length and prescribed diameter by subdivision, characterized in that the resistance to pulling of the filter rods is adjusted to the desired value by more or less dilution of the volatile impregnating agent with water.

34. The method defined in claim 4 in which the agent is acetone.

35. The method defined in claim 5 in which the agent is diethyl ether.

36. The method defined in claim 7 in which the agent is ethyl chloride 37. The method defined in claim 7 in which the agent is chloroform.

38. The method defined in claim 7 in which the agent is carbon tetrachloride.

39. The method defined in claim 8 in which the agent is acetic acid ethyl ester.

40. The method defined in claim 18 in which the additive is selected from the group consisting of tartaric acid and citric acid.

References Cited UNITED STATES PATENTS 3,226,280 12/1965 Muller 156510 BERNARD STICKNEY, Primary Examiner U.S. Cl. X.R. 

